Coiled-filament incandescent lamp



1,637,034 Ju y 1927- J. BERGMANS comm: FILAMENT INCANDESCENT LAMP? Filed Dec. 4, 1923 I ihVentdr: Jam Bergmams,

His Attofiney.

Patented July'ZG, 1927.

UNITED STATES 1,637,034 PATENT OFFICE.

JAN BERGMANS, OF EINDHOVEN, NETHERLANDS, ASSIGNOR, BY MESNE ASSIGN- MENTS, TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

COILED-FILAMENT INCANIDESCENT LAMIIIE'.

Application filed December 4, 1923, Serial No. 678,515, and in the Netherlands and France December This invention relates to improvements'in gasfilled electric incandescent lamps having helically wound filaments of tungsten for example and more particularly to projection lamps of this type.

It is known that in lamps of the aforesaid type great difiiculty is caused by the point of connection between the filament and the leads and consequently a high percentage of such lamps fail by breakage -of the filament near the point of connection. This breakage may be due to mechanical causes such as vibrations or shocks but particularly to discharges occurring across the gas between the ends of the filament or those parts of the leads which are in connection with them and which are heated to a high temperature. The disadvantage oI undue discharges can be obviated by taking care that the parts of the filament that are heated to a very high temperature are not in direct connection with the leads so that the latter remain rather cold. It has therefore already been proposed to stretch'the ends of the helically wound filament that are connected to the leads in order to ensure that the stretched parts owing to the heat conduction of the gas assume a materially lower temperature than the incandescent coil, but this expedient does' not improve the attachmentof the lilament to the leads from a mechanical point of view. a

According to the present invention the ditficulty above described is obviated by disposing each end of the helically wound filament around a mandril of a metal or a metal alloy having a high melting point whereupon the said ends together with the mandril are fixed to the leads preferably by welding. If the filament is made of tungsten, the mandril is preferably made of tungsten or molybdenum.

This method has the following very important advantages. The mechanical attaclnnent of the filament to the lead is proved as the latter near the leads is surported by the mandril. Those parts of the leads that are fixed to the ends of the filament remain rather cold owing to the great increase in efiect of the cross section of the coil near the leads. I

In this case an attachment of the incan descent filament to the leads by welding has particular advantages. As a rule the attachment of the filament by welding is more advisable than by pinching it in the bent ends of the leads, particularly int-he case of filaments having a rather considerable diameter-such for example as are frequently tound inprojecti-on lamps. When welding however a filament of tungsten to a lead of nickel, a tungsten-nickel alloy is produced which in many cases has a materially lower melting point than tungsten and thus the point of connection between the filament and the leads is weakened. When proceeding in accordance with the invention the lowering of the melting point is not troublesome because the ends of the leads remain at a low temperature. When using a mandril welding ensures not only a good attachment of the filament to the leads but also a good contact between the filament and the mandril.

According to the invention the leads may also be disposed in such a manner that those parts to which the ends of the filament together with the mandrils are fixed are more widely spaced than in case of fixing the filament directly to the leads and thus the risk of gas discharges is further decreased.

In the lamps the filament of which comprises a number of coils which are substantially vertical during the normal operationof the lamp, the 'helically wound ends of the filament may according to the present invention be disposedaround mandrils of a metal or a metal alloy having ahigh melting point, such for example as tungsten or molybdenum and together with the mandrils they may be fixed to the pole wires, those parts of the leads that are fixed to the end of the filament being located on the upper lateral side of the filament.

The coils of the filament may be parallel or they may be V-shaped and situated side by side in a plane surface or in a curved surface or again they may be arranged one behind the other in various planes as is the practice for example in projection. lamps.

The ends of the filament thatare dis-' posed around the lnandrilmay preferably be arranged substantially normally to that way of tungsten, which is cated on the lower lateral side of the filament as otherwise their temperature increases toomuch. This arrangement however is objectionable as it is not possible for those wire coils directly connected with the poles to sag freelyfso that ad acent coils may contact with each other and thereby cause the lamp to deteriorate. ln the arragement according to the present invention, the ends of the leads are spaced from the illuminant proper and moreover they are substantially outside the hot flow of gas rising from the illuminant so that they remain rather cold although they are arranged on the upper lateral side of the illuminant.

The accompanying drawing illustrates by example an embodiment of a projection lamp according to the present 111- vention. In the said drawing:

Figure 1 is a front elevation of a projection lamp inwhich those parts, of the leads that are connected to the ends of the filament are arranged onthe upper lateral side-of the illuminant.

Figure 2 is a side elevation of the illuminant with the leads and of the suspension device of the illuminant, and

Figure 3 is a detail on a large scale of the attachment of the illuminant to the lead.

The lamp shown in Figure 1 comprises a sealed glas bulb 1 into which a stem 2 is sealed. 'lwo leading-in wires connected to leads 4 and, 5 of nickel for example, are sealed in the clamped portion of the stem. A filament 6 is connected to the leads, its helically wound ends 7 and 8 being disposed around mandrils 11 of some metal, such as substantially as refractory as the filament and together with the latter welded to the leads. The two mandrels are, as best shown in Figure 1, mounted on the leads to project toward each other in the plane of the leads and be end to end.

The stem 2 supports also the glass rod 3 which is bent in the manner shown in Figure 2. The filament 6 which consists of V-sh'aped coils arranged side by side in a plane surface in the plane of the leads is suspended by means of two intermediate bends of the ll-shaped wire on two hooks 9 of molybdenum for example. .On the lower side any displacement in the transverse direction'of the illuminant is prevented by hooks 10 which may likewise be of molybdenum. It "is however possible for the lower parts of the filament-to move freely upwards and downwards in the said hooks and consequently the coils which, are

suspended between the ends of the mandrels are free to sag and to shrink without there being a risk of some ad'acent coils contacting with'each other. he ends 7 and 8 of aeaaoaa the filament which are wound on the mandrils are arranged approximately normally to the active light giving coils ofthe filament 6 that are not disposed around the -mandril. This arrangement ensures that the points of contact of the filament with the leads are more widely spaced than in the case of the leads being directly connected to the ends of the filament proper and thus there is still less probability of discharges a occurring across the gas between the leads.

In Figure 3, 5 is the end ofthe lead. The helically wound end 8' of the filament is disposed on a mandrilll of tungsten for example which has preferably the same diameter as the mandril used when coiling the filament so that the mandrel is telescoped into the end of the coiled filament. l he end 8 together with the mandril l1 are connected to the lead by welding. By the passage of the current the filament 6 is heated to a bright white heat but the part 8 remains quite dark and consequently also the end 5 of the lead remains rather cold during the time the lamp is burning.

What I claim is 1. An incandescent lamp comprising a sealed envelope containing a .pair of leads, a

coiled metal filament, and a pair of cylindrical mandrels of metal substantially as refractory as said filament and telescoped into the ends of said coiled filament, each of said mandrels and the adjoining end of said filament being Welded to one of said leads whereby saidmandrels project from said leads end to end and in the plane thereof, an intermediate portion of said filament being suspended between the ends of said mandrels and in the plane of said leads.

. 2. An incandescent lamp comprising a sealed envelope containing a pair of leads. a coiled tungsten filament, and a pair of cylindrical tungsten mandrels telescoped into the ends of said filament and welded at their ends to said leads and to'the ends of said filament to project from said leads end to end and in the plane of said leads, the intermediate portion of said filament being bent into coiled sections side by side in the plane of said leads.

3. An incandescent lamp comprising a sealed envelope containing a pair of leads. a coiled tungsten filament, and a pair of cylindrical tungsten mandrels telescoped in- 

